1. Field of Use
This invention relates generally to heating systems and in particular to a flameless heating system for the operator's cab of machines, such as material handling machines, construction machines, mobile cranes, overhead cranes, trucks, tractors, or the like.
2. Description of the Prior Art
In machinery of the aforesaid character, it is important to provide a heating system for the operator's cab, and the prior art discloses several types. For example, electric heating systems employ a red-hot electrical resistance wire as the heat source and use a fan to distribute heat throughout the cab. Combustion-type heating systems use an enclosed flame, fueled by gasoline or fuel oil, for example, and a fan to distribute the heated air (see U.S. Pat. No. 2,567,143, for example). Several forms of flameless heaters also exist which extract heat by means of heat exchangers from heated fluids (such as coolant water or lubricating oil) supplied from an internal combustion engine used to propel and operate the machine. Some flameless heaters depend on expansion/compression of compressible fluids to provide heat which is then distributed by a heat exchanger (see U.S. Pat. Nos. 3,365,133; 3,259,317; 3,214,100). All such prior art heating systems having certain disadvantages. For example, it is undesirable to employ machinery having heaters using red-hot wires or open flames in hazardous environments such as chemical plants, paint plants or other explosive atmospheres. On the other hand, prior art flameless heaters which depend on heated fluids (such as water or oil) supplied from an engine are ineffective unless the engine is in operation. Furthermore, those heating systems which depend on compression/expansion of compressible fluids can be unduly complex and expensive and may require frequent servicing because of fluid losses.
In machinery which is hydraulically operated, i.e., that in which an internal combustion engine or electric motor drives one or more hydraulic pumps to supply hydraulic motors which operate machine components, it is known that heat is generated in the hydraulic system as a result of dumping a liquid, such as hydraulic fluid, water, or oil, from a higher to a lower pressure without doing mechanical work, i.e., as when liquid bucks a system relief valve or because of normal pressure losses resulting from the hydraulic fluid flowing through system piping, valving, etc. This phenomena is described in detail at pages 32 and 33 of the "Fluid Power Data Book" First Edition, 3rd printing 1967, published by Womack Machine Supply Company, 2010 Shea Road, P.O. Box 35027, Dallas, Tex. 75235. However, this publication is concerned with the dangers of fluid overheating and heat build-up and teaches dissipation of excessive heat to atmosphere by means of oil tanks or oil coolers. Insofar as applicant is presently aware, the prior art contains no teaching to employ these principles for a heating system in the operator' s cab of a hydraulic machine or the like.